Multiple compartment grinding mills

ABSTRACT

A grinding mill is disclosed having a cylindrical shell for rotation about its central axis and a division head that divides the interior of the shell into axially disposed compartments, one compartment containing steel rods for relatively coarse grinding and another compartment containing steel balls for finer grinding. The division head is an assembly of elements in which a pair of the elements are annular bulkheads perpendicular to the central axis and spaced apart from each other. The annular bulkhead on the coarse grinding side of the division head assembly defines a central opening of smaller diameter than the central opening defined by the annular bulkhead on the fine grinding side of the division head assembly. A liner extends between the radially inner peripheries of the two annular bulkheads and defines a central passage through the division head assembly with a surface having the configuration of a truncated cone with its central axis coincident with the central axis of the shell and with its apex end pointed toward the coarse grinding compartment. A shielding disk is concentrically mounted within the conical central passage in a plane perpendicular to the shell axis and supported by a plurality of arcuately spaced mounting blocks between the outer periphery of the shielding disk and the inner periphery of the conical central passage. The shield blocks a mass of grinding balls which tends to surge from the ball compartment toward the rod compartment during periods of mill acceleration at startup and during periods of deceleration when being stopped. The normal flow of pulp from the rod compartment into the ball compartment passes through the passage in channels between the mounting blocks and radially outward of the shielding disk.

United States Patent [72] inventor Eugene P. Waddell Brooktield, Wis.

[21 1 Appl. No. 884,149

[22] Filed Dec. I1, 1969 Nov. 30, 1971 Allis-Chalmers ManufacturingCompany Milwaukee, Wis.

[45] Patented [73] Assignee [54] MULTIPLE COMPAR'IMENT GRINDING MILLS 4Claims, 3 Drawing Figs.

Primary Examiner-Andrew Juhasz Assistant Examiner-Gary L. SmithAttorneys- Arthur M. Streich, Robert B. Benson and John P.

Hines ABSTRACT: A grinding mill is disclosed having a cylindrical shellfor rotation about its central axis and a division head that divides theinterior of the shell into axially disposed compartments, onecompartment containing steel rods for relatively coarse grinding andanother compartment containing steel balls for finer grinding. Thedivision head is an assembly of elements in which a pair of the elementsare annular bulkheads perpendicular to the central axis and spaced apartfrom each other. The annular bulkhead on the coarse grinding side of thedivision head assembly defines a central opening of smaller diameterthan the central opening defined by the annular bulkhead on the finegrinding side of the division head assembly. A liner extends between theradially inner peripheries of the two annular bulkheads and defines acentral passage through the division head assembly with a surface havingthe configuration of a truncated cone with its central axis coincidentwith the central axis of the shell and with its apex end pointed towardthe coarse grinding compartment. A shielding disk is concentricallymounted within the conical central passage in a plane perpendicular tothe shell axis and supported by a plurality of arcuately spaced mountingblocks between the outer periphery of the shielding disk and the innerperiphery of the conical central passage. The shield blocks a mass ofgrinding balls which tends to surge from the ball compartment toward therod compartment during periods of mill acceleration at startup andduring periods of deceleration when being stopped. The normal flow ofpulp from the rod compartment into the ball compartment passes throughthe passage in channels between the mounting blocks and radially outwardof the shielding disk.

MULTIPLE COMPARTMENT GRINDING MILLS CROSS-REFERENCE TO RELATED PATENTAPPLICATION This invention is disclosed and described as being appliedto a mill which is the subject of a Pat. application of Raymond C..lenness and Wayne C. Dannenbrink, Ser. No. 884,059 filed Jan. 26, 1970.

BACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates to multiple compartment cylindrical grinding mills having acompartment containing steel rods for coarse grinding and a compartmentcontaining steel balls for finer grinding, and in particular to adivision head assembly between the compartments.

2. Description of the Prior Art Grinding mills having a cylindricalshell divided into longitudinally disposed compartments by a divisionhead assembly, are shown in prior art patents such as U.S. Pat. No.2,052,426 of 1936; U.S. Pat. No. 3,144,212 of 1964; and U.S. Pat. No.3,298,619 of 1967. The aforementioned U.S.Pat. No. 2,052,426 alsodiscloses a division head assembly having a pair of spaced annularbulkheads, and a conical liner connected on its apex end to the centralopening in each of the annular bulkheads of the division head assembly.In this prior art patent the conical liner connected to the coarse sidebulkhead does not extend to the fine side bulkhead. Such an arrangementprovides for pulp in both compartmentsflowing into a central dischargechamber rather than a one direction through-flow movement of pulp fromthe coarse grinding compartment, through the division head assembly, tothe fine grinding compartment. With central discharge mill, rather thana one direction end to end movement of pulp, much greater classifiercapacity must be provided because. partly ground material which needsfurther grinding and finely ground material needing no further grinding,are mixed and discharged together through a common discharge port in acentral portion of the mill.

For a one direction through-flow movement of pulp requiring lessclassifier capacity, the prior art discloses division head assembliesand mill arrangements such as are disclosed in U.S. Pat. Nos. 3,144,212and 3,298,619. However, in actual practice utilizing such mills withsuch division head assemblies, which include a slotted bulkhead on thefine grinding side of the division head, pieces of the steel grindingballs are forced through the slotted bulkhead and into the coarsegrinding compartment containing steel grinding rods. Such pieces in therod compartment get between rods and hold the rods apart, not allowingthem to come sufficiently close together to break pulp material andthese prior art constructions therefor, like the central dischargemills, also have disadvantages.

The copending Pat. application of Raymond C. Jenness and Wayne C.Dannenbrink, Ser. No. 884,049 filed Jan. 26, 1970, a grinding mill isdisclosed having a cylindrical shell for rotation about its central axisand a division head that divides the interior of the shell into axiallydisposed compartments, one compartment containing steel rods forrelatively coarse grinding and another compartment containing steelballs for finer grinding. The division head is an assembly of elementsin which a pair of the elements are annular bulkheads perpendicular tothe central axis and spaced apart from each other. The annular bulkheadon the coarse grinding side of the division head assembly defines acentral opening of smaller diameter than the central opening defined bythe annular bulkhead on the fine grinding side of the division headassembly. A liner extends between the radially inner peripheries of thetwo annular bulkheads and defines a central passage through the divisionhead assembly with a surface having the configuration of a truncatedcone with its central axis coincident with the central axis of theshell, and with the apex end of the configuration pointed toward thecoarse grinding compartment. Such a conical configuration of the centralopening through the division head from the rod compartment to the ballcompartment eliminates the need for slotted openings in one of thebulkheads and provides a downwardly sloped path from the coarse grindingchamber to the fine grinding chamber. During normal operation of themill the slope of the path prevents balls moving through the divisionhead from the ball compartment into the rod compartment because duringnormal operation the grinding balls cannot roll up the slope. Balls thatenter the rod compartment via a path external to the shell as in closedcircuit grinding, can roll down the slope from the rod compartment backto the ball compartment. However, while such a division head doesprovide the described result during normal operation, during periods ofmill acceleration at startup and during periods of deceleration when themill is stopping, the charge of grinding balls in the fine grindingcompartment tends to surge toward the division head. During such periodsthe grinding balls could move up the slope of the central passagethrough the division head and enter the rod compartment where theyinterfere with the grinding action of the rods. It is to this problemthat the present invention is directed and the provision of a solutionto this problem is a principal object of the present invention.

SUMMARY OF THE PRESENT INVENTION In a preferred embodiment of thepresent invention, as applied to a mill such as disclosed in theaforementioned Jenness and Dannenbrink patent application and which hashereinbefore been described, a shielding disk is concentrically mountedwithin the conical central passage through the division head assembly.The disk is arranged in a plane perpendicular to the shell axis and issupported by a plurality of arcuately spaced mounting blocks between theouter periphery of the shielding disk and the inner periphery of theconical central passage. The shielding disk blocks the surge of ballsfrom moving into the rod compartment during acceleration anddeceleration while the normal flow of pulp from the rod compartment tothe ball compartment during normal operation of the mill, passes throughchannels between the mounting blocks and radially outward of theshielding disk.

Other features and objects of the invention that have been attained willappear from the more detailed description to follow with reference to anembodiment of the present invention shown in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the accompanying drawingshows a side elevation, in section, a grinding mill according to thepresent invention;

FIG. 2 shows to enlarged scale, a portion of a division head assembly inFIG. 1; and

FIG. 3 is an end view of the portion of the division head assembly shownin FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The multistage grinding milldisclosed in FIG. 1 of the drawing comprises in general a rotarycylindrical shell casing 1 illustrated as having uniform orsubstantially uniform diameter throughout its length, the casing beingprovided with feed and discharge end heads 2, 3, respectively. Thecasing 1 is divided into a pair of grinding chambers 4 and 5 in a mannerand by structure that will be described in detail later. The chamber 4on the inlet end of the casing l is provided with a plurality of rods 6that provide for relatively coarse grinding in the chamber 4. Thechamber 5 is provided with a plurality of balls 7 for relatively finegrinding of material in the chamber 5. The mill is rotatably mounted insuitable end bearings which carry feed and discharge trunnions 11 and12, respectively. Rotary motion about its horizontal central axis isimparted to the mill by means of power applied to a driving gear 13secured either around the inlet end of the casing 1 as shown or aroundthe feed trunnion (not shown). The feed end of the mill is provided witha feeder such as feeder 15 for introducing the material which is to bereduced into the inlet end of the coarse grinding chamber 4 through thefeed trunnion ll.

The discharge end of chamber 5 is provided with a perforated plate .19which is spaced from the end head 3. Located within the space betweenplate 19 and the end head 3 is a series of elevating vanes 20. The innerextremities of the elevating vanes 20 are located close to a centraldischarge cone 21, the apex of which is directed toward the dischargetrunnion l2.

The arrangement shown in FIGS. 1 and 2 for dividing the casing 1 intothe two grinding compartments 4 and 5, includes an arrangement of partsshown to enlarged scale in FIG. 2 and FIG. 3. A division head assemblyis mounted within the mill comprising a pair of spaced annular bulkheads26, 27. The side of bulkhead 26 facing the feed head 2 and the side ofbulkhead 27 facing the discharge head 3, are each provided withreplaceable wear liners 28, 29 respectively. Liner 29 projects fartherradially inward than does bulkhead 27 but the reverse is true on theopposite side of the division head assembly where the liner 28 does notproject as far radially as bulkhead 26 thus leaving an inner portion ofbulkhead 26 unprotected by liner 28. The inner portion of bulkhead 26not protected by liner 28 is however covered and protected by a liner 30having both a radial portion 31 and an axially extending portion 32. Aliner extends between the axial extending portion 32 of liner 30 and theradially inner portion of liner 29, and portion 32 and liner 35 togetherprovide and define a central passage 36 through the division headassembly 25 having openings 37, 38 and a configuration therebetween of atruncated cone with its apex end pointed toward the feed head 2 end ofthe mill and a base flange 39 on the end thereof facing the dischargehead 3.

Shielding means comprising a disk 40 is mounted concentrically withinthe central passage 36 and perpendicular to the central axis -xx' Aplurality of mounting blocks 41 are connected to the outer periphery ofdisk 40, as by welding, and blocks 41 are connected to the innerperiphery of liner 35 by bolts 42 that pass through blocks 41, liner 35,bulkhead 26 and liner 30 to unite the assembly of those parts. Aperipheral pulp channel 43 is defined between each adjacent pair ofblocks 41, the outer circumference of disk 40 and an intermediatediameter on the inner surface of liner 35 indicated in FIG. 3 by thebroken line circle 44.

In the operation of the mill assembly that has been described, materialto be ground is delivered to the feeder such as feeder 15 and fed intothe coarse grinding chamber 4 where the rods 6, which tumble as gear 13turns casing 1, provide a preliminary grinding of the feed material toprovide a coarse pulp which will overflow from chamber 4 through thepassage 36 in the division head assembly 25, and into chamber 5. Inchamber 5 the steel balls 7 tumble and provide a further grinding actionto provide a finer pulp which flows through the perforated plate 19 tobe picked up by the vanes 20 and dumped into the discharge cone 21. Withthe central passage 36 through division head assembly 25 being definedby liner 35 and portion 32 of liner 30, which in turn provide aconfiguration of a truncated cone with its central axis coincident withthe central axis of the mill shell 1 and with the apex end of thisconfiguration pointed toward the chamber 4, the bottom surface of this.passage 36 is sloped downwardly from the chamber 4 toward chamber 5.Thus in normal operation (i.e., steady speed neither accelerating nordecelerating) balls 7 do not roll up this inclined surface and they arekept out of the rod compartment 4, but balls or pieces of balls that getinto chamber 4 via an external recirculation circuit (not shown) canroll out of chamber 4 into chamber 5 where they should be.

During periods when the mill is being started and being accelerated tooperating speed and when the mill is being slowed in preparation forshutdown, surges of grinding balls toward the division head assembly 25are prevented from passing through the passage 36 to the rod compartment4, by the shielding disk 40. During normal operation of the mill whenthe mill IS being rotated at steady and constant rate, pulp flows freelyfrom the rod compartment 4, through the channels 43 and into the ballcompartment 5.

From the foregoing detailed description of the present invention, it hasbeen shown how the objects of the invention have been attained in apreferred manner. However, modifications and equivalents of thedisclosed concepts such as readily occur to those skilled in the art areintended to be included within the scope of this invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a grinding mill having a cylindrical shell mounted for rotationabout its central axis, a compartment containing media for coarsegrinding and a compartment containing media for finer grinding separatedby a division head assembly, said division head assembly comprising afirst and a second annular bulkhead perpendicular to said axis andspaced apart from each other, the annular bulkhead on the coarsegrinding side of the division head assembly defining a central openingof smaller diameter than a central opening defined by the annularbulkhead on the finer grinding side of the division head assembly, anaxially extending liner extending between and connected to the radiallyinner peripheries of the first and second bulkheads and with said linerhaving an inner surface defining a central passage through the divisionhead assembly with a surface having a configuration of a truncated conewith a central axis coincident with the central axis of the shell andwith an apex end pointed toward the coarse grinding compartment, andshielding means within said central passage presenting a surfaceblocking a central portion of said passage and defining arcuateperipheral channels therethrough to block surging masses of finegrinding media from passing therethrough into the coarse grindingcompartment and provide pulp channels therethrough from the coarsegrinding compartment to the fine grinding compartment.

2. The structure of claim 1 characterized in that both annular bulkheadsare imperforate thus making the channels defined within the centralpassage the sole path of communication within the shell between the twocompartments.

3. ln a grinding mill having a cylindrical shell mounted for rotationabout its central axis, a compartment containing rods for coarsegrinding and a compartment containing balls for finer grinding separatedby a division head assembly, said division head assembly comprising afirst and a second annular bulkhead perpendicular to said axis andspaced apart from each other, the annular bulkhead on the rodcompartment side of thedivision head assembly defining a central openingof smaller diameter than a central opening defined by the annularbulkhead on the ball compartment side of the division head assembly, anaxially extending liner extending between and connected to the radiallyinner peripheries of the first and second bulkheads and with said linerhaving an inner surface defining a central passage through the divisionhead assembly with a surface having a configuration of a truncated conewith a central axis coincident with the central axis of the shell andwith an apex end pointed toward the rod compartment, a shielding diskconcentrically mounted within said central passage and perpendicular tosaid central axis, and a plurality of mounting blocks connecting thedisk to the liner and supporting the disk to block a central portion ofthe central passage and provide a plurality of arcuate pulp channelsbetween the outer periphery of the disk and the inner periphery of theliner.

4. The structure of claim 3 characterized in that the disk has adiameter larger than the central opening defined by the annular bulkheadon the rod compartment side of the division head assembly and smallerthan the central opening defined by the annular bulkhead on the ballcompartment side of the division head assembly.

1. In a grinding mill having a cylindrical shell mounted for rotationabout its central axis, a compartment containing media for coarsegrinding and a compartment containing media for finer grinding separatedby a division head assembly, said division head assembly comprising afirst and a second annular bulkhead perpendicular to said axis andspaced apart from each other, the annular bulkhead on the coarsegrinding side of the division head assembly defining a central openingof smaller diameter than a central opening defined by the annularbulkhead on the finer grinding side of the division head assembly, anaxially extending liner extending between and connected to the radiallyinner peripheries of the first and second bulkheads and with said linerhaving an inner surface defining a Central passage through the divisionhead assembly with a surface having a configuration of a truncated conewith a central axis coincident with the central axis of the shell andwith an apex end pointed toward the coarse grinding compartment, andshielding means within said central passage presenting a surfaceblocking a central portion of said passage and defining arcuateperipheral channels therethrough to block surging masses of finegrinding media from passing therethrough into the coarse grindingcompartment and provide pulp channels therethrough from the coarsegrinding compartment to the fine grinding compartment.
 2. The structureof claim 1 characterized in that both annular bulkheads are imperforatethus making the channels defined within the central passage the solepath of communication within the shell between the two compartments. 3.In a grinding mill having a cylindrical shell mounted for rotation aboutits central axis, a compartment containing rods for coarse grinding anda compartment containing balls for finer grinding separated by adivision head assembly, said division head assembly comprising a firstand a second annular bulkhead perpendicular to said axis and spacedapart from each other, the annular bulkhead on the rod compartment sideof the division head assembly defining a central opening of smallerdiameter than a central opening defined by the annular bulkhead on theball compartment side of the division head assembly, an axiallyextending liner extending between and connected to the radially innerperipheries of the first and second bulkheads and with said liner havingan inner surface defining a central passage through the division headassembly with a surface having a configuration of a truncated cone witha central axis coincident with the central axis of the shell and with anapex end pointed toward the rod compartment, a shielding diskconcentrically mounted within said central passage and perpendicular tosaid central axis, and a plurality of mounting blocks connecting thedisk to the liner and supporting the disk to block a central portion ofthe central passage and provide a plurality of arcuate pulp channelsbetween the outer periphery of the disk and the inner periphery of theliner.
 4. The structure of claim 3 characterized in that the disk has adiameter larger than the central opening defined by the annular bulkheadon the rod compartment side of the division head assembly and smallerthan the central opening defined by the annular bulkhead on the ballcompartment side of the division head assembly.